There has been disclosed a heat-resistant catalyst in which palladium is supported, as an active constituent, on a carrier which is mainly made from a composite oxide of aluminum and lanthanum. It has been reported that such a catalyst exhibits high methane combustion reactivity even after the catalyst is baked at 1200° C. for 3 hours (see Patent Literature 1, for example).
Further, it has been disclosed that a carrier which is made from (i) a composite oxide of Al2O3 derived from aluminum alkoxide, (ii) CeO2, and (iii) La2O3 has a high surface area stability, and a catalyst in which a precious metal is supported on the carrier exhibits a high purification capability for a simulated automobile exhaust gas (see Patent Literature 2, for example).
In addition, it has been disclosed that a catalyst suppresses growth of metal particles and growth of particles of an oxygen occlusion/release material, the catalyst being such that (i) a carrier is made from a porous oxide derived from aluminum alkoxide, (ii) the carrier and the oxygen occlusion/release material are mixed with each other at an atomic level so as to form a composite oxide, and (iii) the metal is supported on the composite oxide (see Patent Literature 3, for example).
Further, it has been described that (i) a Pt/SiO2 catalyst produced by a sol-gel method has Pt particles coated with SiO2, and (ii) the catalyst can therefore inhibit sintering of the Pt particles (see Non-Patent Literature 1, for example). In addition, it has been described, as to the Pt/SiO2 catalyst produced by the sol-gel method, that (i) there is high interactivity between the Pt particles and the coating SiO2, and (ii) the Pt particles and the coating SiO2 therefore form a compound such as a Pt—Si alloy or a Pt3Si (see Non-Patent Literature 2, for example).
Moreover, it has been disclosed that Pd is equally dispersed and heat deterioration can be suppressed in a case where (i) a Pd solution is mixed with a solution in which aluminum alkoxide and hexylene glycol are mixed with each other, and (ii) hydrolysis of alkoxide is then carried out (see Patent Literature 4, for example).
Further, it has been known that rhodium is mixed in alumina and forms a solid solution in combination with alumina, when the catalyst in which rhodium is supported on alumina is subjected to a high-temperature process. In this regard, there has been disclosed a method for recovering rhodium, in which an element is added to alumina so as to inhibit rhodium from being mixed in alumina (i.e. inhibit rhodium from forming the solid solution in combination with alumina), the element being selected from the group consisting of lanthanum, calcium, lead, and sodium (see Patent Literature 5, for example).